Correct answer : a Acetylcholine receptor
Myasthenia gravis is a type II hypersensitivity disorder caused by antibodies that bind to the acetylcholine receptor.
These antibodies interfere with the transmission of neural impulses at the neuromuscular junction, causing muscle weakness and easy fatigability. External ocular and eyelid muscles are most often affected, but the disease is often progressive and may cause death by respiratory muscle paralysis.
Autoantibodies to desmoglein-3 are found in patients with pemphigus vulgaris, an autoimmune blistering skin disorder.
Antibodies to the TSH receptor are seen in patients with Graves hyperthyroidism.
Antibodies to calcium channels are found in patients with Eaton-Lambert syndrome. This paraneoplastic syndrome also manifests as muscle weakness but is usually associated with small cell carcinoma of the lung.
Rheumatoid factor represents multiple antibodies directed against the Fc portion of IgG and is seen in patients with rheumatoid arthritis and many other collagen vascular diseases.